Retirement slammed Carole Jacko. Raising two grandchildren, she's too young for Medicare and too strapped to pay $600 a month for health insurance.

So when a trip to the emergency room ended with a diagnosis of diabetes, Jacko found a creative solution.

She became a medical guinea pig, offering herself to science in exchange for free medication, free doctor's visits and even a modest payment.

"It really covers costs," Jacko said. And the clinic staffers "are very good and professional. They keep a good eye on you."

With the economy careening and millions uninsured, some doctors and researchers believe the lure of volunteering for medical research is growing – and so are potential ethical pitfalls.

"Sometimes desperation leads people to be poor shoppers," to gloss over risks or grasp at imagined benefits, said Kevin Weinfurt, a Duke University professor who focuses on medical decision-making and ethics.

No regulations limit how much a person can be paid to take part in medical research.

Payments are often modest, however, usually intended to cover gasoline, time or inconvenience. But the odd $25 here or $50 there can be dwarfed by the value of free medical care that would otherwise cost hundreds or thousands of dollars.

S. Elena MacLachlan, an Oakland nurse studying for her doctorate, is willing to undergo what might be a sham surgery for the chance to get a new type of weight-loss operation for free.

"I'm not in poverty. I have a good career. But my insurance doesn't cover it," she said, estimating a similar operation would cost her tens of thousands of dollars otherwise. "I thank God for this."

Researchers do not agree on how much money it takes to cross the line and exert "undue influence" or coercion to get someone to enroll in a study. That's something federal regulations do forbid.

"This is the most complicated issue in research ethics, and it's still an unsettled question," Weinfurt said.

It has lingered for more than 100 years, since an Army surgeon named Walter Reed paid volunteers at a Cuban outpost $100 in gold to risk being infected with yellow fever. The men got another $100 if they contracted the disease, payable to themselves – or any designated survivor.

The dangers Carole Jacko runs are far less dramatic.

She is participating in a study aimed at evaluating how three different high blood pressure medications work together. The combination being studied is approved in Europe, but not by the U.S. Food and Drug Administration. Even so, U.S. doctors can and sometimes do prescribe the combination already – but drug companies are not allowed to promote such "off label" uses.

Jacko signed a thick disclosure packet that detailed known side effects of each drug, including nausea, headaches and kidney problems. More ominously, she was warned, she would have to stop taking all medications during a "wash-out" period before the start of the study, leaving her high blood pressure temporarily uncontrolled.

That, she was told, carried a rare chance of a fatal or disabling stroke or heart attack.

"It really didn't scare me," she said, because she knew and trusted the medical assistants who saw her regularly.

With arthritis, diabetes and high blood pressure, Jacko, 60, can offer herself up again and again for a variety of research.

In one study, her blood pressure soared during the wash-out period. Clinic staffers monitored her closely, she said, and eventually gave her the option to switch to a different research project.

Now, she's back for more.

Every few weeks she drives from the Citrus Heights home she shares with her son's family to the offices of Dr. John Champlin in Carmichael. She rolls up her sleeve for a blood pressure check, gets her blood drawn, and leaves with a new supply of medication and a $45 check – payment to her for that day's office visit.

"I have no medical insurance," Jacko said. "This is a way for me to have blood tests and not have to pay the high lab costs. This worked out really well for me."

Champlin hasn't added up the numbers, but he thinks he's getting more patients like Jacko as people lose jobs and cannot afford insurance.

As a primary care doctor specializing in patients who pay cash, Champlin has seen people who have to choose between medical care and groceries, who have to borrow from relatives to scrape up money for a potentially lifesaving test.

So he tries to counsel patients on which tests they might safely postpone for a while. He helps negotiate discounts on tests needed right away. And he guides some patients to medical studies, which make up about 15 percent of his practice.

"There is a downside to this," Champlin said. Some people who hoped to get useful medication end up getting a sugar pill or other placebo that does them no good.

Others, though, benefit greatly. Sometimes the routine tests given to research subjects spot underlying problems, from diabetes to cancer. Sometimes the studies use no placebos, because they compare standard medications with newer ones.

Along with Jacko, study participants in Champlin's practice include Don Munoz of Sacramento, who turns to medical research for stopgap care because he's uninsured, and Cheryl Cass of Carmichael, whose insurance carries a high deductible.

Then there's Marie McAmis of Fair Oaks, who has insurance and enrolls in studies partly to get access to cutting-edge treatments – and to save money on co-payments.

Once, she was notified that a study she participated in was halted because a medication involved caused tumors in mice.

"I didn't get worried about it or anything," McAmis said, because unlike the mice, she was in the study for a relatively short time and might have gotten a placebo.

So far, no one is tracking whether more people are becoming research subjects to save money on health care, but that would be "a very possible result of our economic situation," said Christine Grady, deputy chief of bioethics at the National Institutes of Health.

Grady has studied research compensation for years, and thinks that paying research subjects for their time and trouble is simply respectful – as long as they know what they're getting into.

"What people worry about is if you make the amount too much, some people will either ignore the risks or sort of be blinded to the risks," Grady said.

The solution to that, she thinks, is to make disclosures so detailed and clear that people can size up their own situation and make the best choices for themselves.

It's also important to remember that such choices don't take place in a vacuum, said bioethicist Weinfurt.

"The broader, ethical challenge for the society is that so many people do not have insurance for these basic health care needs," he said. "Given that this is the situation, I can imagine plenty of cases where people understand the nature of the research and they're being quite rational joining the study to get what they want."